Aircraft landing gear are generally arranged to provide suspension and shock absorbing functions for the aircraft during landing and take-off. The suspension and damping functions may be provided in a single suspension strut in each landing gear. In such struts the suspension spring is commonly provided by one or more gas springs and damping is provided by hydraulic fluid. In use, a proportion of the gas or the hydraulic fluid escapes and needs to be replenished to a predetermined level so that the strut meets its required performance criteria.
The level of each of the fluids in a strut is often critical to ensure its correct performance. Servicing of such equipment therefore requires the accurate determination of the levels of the gas and the hydraulic fluid. Without such determination it is not possible to know whether a strut requires servicing or that it has been serviced correctly. In many struts the various fluid levels are not externally visible. As a result, accurate determination of the levels requires the introduction of suitable sensors or elaborate servicing techniques that involve moving the strut into a predetermined configuration and then following a prescribed refilling procedure. Such servicing procedures are time consuming, hazardous and difficult, especially if the strut is part of a large aircraft.